Scanner, printers, and copiers are all examples of image processing systems that process bit information representing colors in the image. The images are represented by pixels, each of which includes bits that represent the colors. For example, in some image processing systems (e.g., a scanner), each pixel is defined by 16 bits that represent the amount of red in the pixel, 16 bits that represent the amount of green in the pixel, and 16 bits that represent the amount of blue in the pixel. Thus, each pixel is represented in these systems by 48 bits.
Scanning a black-and-white document with a color scanner introduces some color into the output, which is due to imperfections in the scanner elements. The spurious color can be objectionable, and a color plane adjustment component can be used to remove the spurious color. In operation, the scanner output for various shades of gray is measured, and an offset value is generated. The offset value is programmed into the color plane adjustment component, and the color plane adjustment component adds the offset value to the values in a three-dimensional color space that represent color (e.g., Cr and Cb values). However, the color plane adjustment component adds this offset to every color value in the three-dimensional color space—not just gray values. For color values that are far from gray, this correction is unnecessary and undesirable.